As disclosed in Japanese Patent Publication JP 2004-307851 A, transparent films made of transparent resins and glass fiber substrates have been proposed as a replacement member for a glass plate utilized in a flat-panel display such as a liquid-crystal display, a plasma display, and an OELD (organic light emitting display).
In order to form these transparent films, for example, a resin composition is prepared by mixing a high refractive resin having refractive index higher than the glass fiber with a low refractive resin having refractive index lower than the glass fiber to have a resultant refractive index approximate to that of the glass fiber. Thereafter, prepregs are prepared by drying the glass fiber substrate impregnated with the prepared resin composition to be half-cured. The transparent film is formed by hot-pressing the prepregs.
A combination of the glass fibers and the matrix resin having refractive index compatible to the glass fiber can avoid undue refraction within the transparent film in order to assure good visibility as required for the display.
Generally, an epoxy resin is used as the resin composition for forming the transparent film. The resin composition is prepared by mixing different kinds of epoxy resins one having the refractive index higher than the glass fiber and the other having the refractive index lower than the glass fiber in order to approximate the refractive index of the resin composition to that of the glass fiber.
In the transparent film in which the epoxy resin is used as the resin composition, the epoxy resin having comparatively high glass transition temperature is used as the high refractive resin in order to improve heat resistance of the transparent film. However, the transparent film made of the epoxy resin having comparatively high glass transition temperature is likely to be discolored into yellow, when heated.